The best explanation for an ABO result pattern showing: anti-A 3+, anti-B 3+, A1 cells 2+, B cells 0; anti-A1 lectin 0; A2 cells 0?

• A. A2 with anti-A1
• B. A2B person with anti-A1
• C. O person with anti-A
• D. AB person with anti-A1

Answer: (B)

Start with what the pattern tells you about the red cells and the plasma. The strong agglutination with both anti-A and anti-B shows the patient’s red cells carry both A and B antigens, so the blood type is AB by forward typing.

Now look at the reverse typing results. A1 cells agglutinate 2+, while B cells do not react. That means the patient’s plasma contains an antibody that reacts with A1 cells but not with B cells—this is anti-A1. The anti-A1 lectin test is negative, indicating the patient’s own red cells are not A1 antigen-bearing. They are A2 instead. The A2 cells showing no reaction fits with anti-A1 not recognizing A2 antigen.

Putting it together: the individual is AB by forward typing, but their red cells are of the A2 subtype, and their plasma contains anti-A1 antibodies that react with A1 but not with A2. This pattern fits an A2B phenotype with anti-A1 in the plasma.